With the ever increasing desire for faster data rates, notably through long-term evolution (LTE) networks, system designers have turned to carrier aggregation. Carrier aggregation increases bandwidth, and thus bitrate, by using multiple carriers to form a larger overall transmission bandwidth. The channels (frequency ranges) of the carriers can either be adjacent or separated by a substantial distance, e.g., being in different frequency bands. The use of carrier aggregation, however, has considerably increased transceiver complexity not only does the transceiver have to generate multiple independent buffered local oscillator (LO) signals, the buffered LO signals also have to be routed to the appropriate transceiver components, thereby increasing the length of the transmission lines carrying the LO signals as well as the routing complexity and density of transmission lines. The LO signals are used by the transceiver to upconvert and downconvert received RF signals to baseband for processing.
Besides problems in fabricating the transceiver due to the complicated routing, the increased routing length further leads to an increase of power consumption by the buffers. Both the increased signal power as well as density substantially increases the crosstalk between the channels. As is known, crosstalk may be caused by undesired capacitive, inductive, or conductive coupling between signal lines in circuitry that results in one or more frequencies present in one signal line appearing as noise in another signal line. In addition to increased signal power and line density, with the wide range of channels being used, an enhanced frequency range of the RF and LO signals is present in the transmissions lines. Buffers with faster slopes are thus used to accommodate the higher frequencies, resulting in increased noise at the baseband from higher order coefficients during mixing to downconvert the received RF signals. The increased coupling between transmission lines causes an undesirable amount of noise in the transceiver, resulting in increased baseband noise which degrades the signal to noise ratio (SNR) of the received RF signals.
It would be therefore desirable to reduce coupling between transmission lines within a chip or in a printed circuit board (PCB), notably in transceivers configured to operate in cellular networks, such as LTE and LTE-A networks using multiple carrier aggregation.